This invention relates generally to X-ray apparatuses and in particular to X-ray target assemblies and X-ray apparatuses incorporating the same.
X-ray target assemblies are used for example in linear accelerators to produce X-rays, which have various applications including in medical radiation therapy and imaging. In operation, incident electron beams strike a target to generate X-rays. As a consequence, the target is heated to elevated temperatures. A target material oxidizes catastrophically at elevated temperatures, thus limiting its useful life. It would be therefore desirable to isolate the target from oxygen during operation.
In conventional linear accelerators, X-ray targets reside either within the vacuum envelope of an accelerator, or in air outside of the vacuum envelope. Target materials would be protected from oxidization if they reside within the vacuum envelope. However, the design for target assemblies residing within the accelerator vacuum envelope is complex due to added vacuum walls and interface considerations. Actuation of targets in vacuum is complicated and any water leaks in the assembly would contaminate the vacuum envelope causing extended downtime of the accelerator.
For target assemblies residing outside of the vacuum envelope, conventional methods for ensuring target longevity include reducing incident electron beam power. Target heating is modest and peak operating temperatures are below critical levels. However, the corresponding dose-rate output is limited due to the reduced beam power and temperature limits in the target materials. Another conventional method is to use oxidation resistant target materials such as gold, platinum, and their alloys. Conventional oxidation resistant materials generally have low strength, thus both the beam power used and corresponding dose rate are limited. In some conventional accelerators, the target assembly is moved during exposure to incident electron beams to reduce volumetric power deposition and peak operating temperatures.
Therefore, while significant achievements have been made, further developments are still needed to provide a target assembly capable of converting focused energetic electrons to ionizing radiation while protecting the heated portion of the target assembly from life-limiting oxidation corrosion.